Abstract

Abstract

Under existing management technology, Lakeland sands
(Typic Quartzipsamments) produce low yields of soybeans
[Glycine max (L.)Merr.] in North Carolina. These
soils have an available water holding capacity of only
4.0% on a weight basis and as a result require about
2.5 cm of water every 5 to 6 days during the growing
season to produce acceptable crop yields. In addition,
Lakeland sands usually have extremely low or a totally
nonexistent indigenous population of Rhizobium japonicum.
Information on irrigation and nodulation effects
is needed to make these soils more productive.

The objectives of this study were to investigate the
influence of irrigation and inoculation with different R.
japonicum strains on yields of soybeans grown in a
Lakeland sand. The study was conducted at the Sandhills
Research Station at Jackson Springs, North Carolina.
Additional nonirrigated plots inoculated with strains
31, 110, and 122 were initiated on finer textured North
Carolina soils for comparative purposes to the Lakeland
sand.

Soil moisture treatments included plots not irrigated
and plots irrigated each week with 2.5 cm of water. The
five inoculation treatments consisted of a set of noninoculated
plots and plots inoculated with strains of R.
japonicum representing serogroups 31, 76, 110, and 122
at the rate of 50 ✕ 104 cells per cm of soybean row.
Numbers of soil rhizobia were monitored throughout the
study using a plant infection and MPN technique.

Irrigated soybean seed yields were significantly greater
when inoculated with rhizobia of either serogroup 110
or 122 than yields from noninoculated but irrigated
plots. Inoculation without irrigation did not increase
soybean yields. It was also observed that inoculated, irrigated
soybeans had greater nodule mass and numbers of
nodules than the nonirrigated and/or noninoculated
plots. All four serogroups used in the study adequately
nodulated soybean roots under irrigation and produced
fewer nodules on soybean roots in the nonirrigated plots.
On the basis of seed yield, strain ranking from best to
worst was: 122>110>31>76. The noninoculated controls
yielded higher than serogroup 76 but less than those soybeans
in plots inoculated with serogroup isolate 31.

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